[Main] change URL

as reported in the forum: https://forum.freecadweb.org/viewtopic.php?p=601657#p601657
we should use our new URL

src/Main/MainGui.cpp

@@ -169,7 +169,7 @@ int main( int argc, char ** argv )
     App::Application::Config()["ExeName"] = "FreeCAD";
     App::Application::Config()["ExeVendor"] = "FreeCAD";
     App::Application::Config()["AppDataSkipVendor"] = "true";
-    App::Application::Config()["MaintainerUrl"] = "http://www.freecadweb.org/wiki/Main_Page";
+    App::Application::Config()["MaintainerUrl"] = "http://www.freecad.org/wiki/Main_Page";
 
     // set the banner (for logging and console)
     App::Application::Config()["CopyrightInfo"] = sBanner;